Government plans to block internet pornography at source, amid concerns about the "premature sexualisation" of children, have prompted a fierce backlash from digital rights campaigners. The proposals have also highlighted how the debate around children and sexual material is increasingly shaped by religious conservatives.

One of the organisations quoted extensively over the last few days is Safermedia, a pressure group campaigning to "reduce the harmful effects of the media on our children, families and society".

Safermedia, formerly known as Mediamarch, supports the "porn lock" proposals and its spokespeople claim academic research substantiates their view that sexual imagery harms children's mental health. But their moral stance is an explicitly Christian one – the group's co-founder Miranda Suit is an organiser for the Christian People's Alliance, and its website cites Saint Paul's epistles to the Philippians and the Ephesians as inspiration for the campaign.

Safermedia is just one of many religiously inspired lobby groups for whom the sexualisation debate has provided an easy route into the media and a veneer of credibility on the left wing.

Some organisations, such as the Society for the Protection of Unborn Children, Care, Christian Concern and Anglican Mainstream (who recently held a conference on "Schools and the sexualisation of our children") are explicit about their scriptural inspiration. The religious origins of other groups – such as the Front Page Campaign and Mediawatch-uk – are not immediately obvious, but a littledigging reveals them. All have wholeheartedly embraced the language of sexualisation, decrying the ready availability of "inappropriate" and "provocative" material, and all are regularly quoted in the media.

Many of these organisations consciously co-opt feminist terminology and attract feminist support by speaking frankly about the "pornification" of popular culture and the effect this may have on the aspirations of young people, particularly girls. But the progressive language conceals a distinctly reactionary political agenda.

The Front Page Campaign, for example, receives widespread support from feminist activists, yet its motivations seem antithetical to feminist aims. It not only calls for the covers of explicit lads' mags to be covered up, but also those of the "growing number of gay magazines for both men and women". The campaign was established by Scottish Mormon Amy King, who in June this year was a guest speaker (alongside Mediawatch's director Vivienne Pattison) at the Family Values conference, an initiative of the Mormon church aimed at promoting "core family values as espoused and taught by the Lord Jesus Christ and His earthly representatives".

Despite the broad range of religious traditions and denominations represented by these groups, their stance on the issue of sexualisation tends to be remarkably similar. For them, the term neatly encapsulates a narrative of moral degeneration that is so broad as to effectively include any representation or discussion of sex, sexuality and relationships, whatever the context. So pornography is harmful, but for some so are gay characters in soaps and adverts for condoms. Their bete noire is sex and relationships education (SRE) in schools – and they vigorously oppose any attempt to bring the subject within the English national curriculum.

For many years these religious lobby groups have been at the fringes of civil society, but the current and previous government's focus on tackling sexualisation has given them a unique opportunity to shape public debate and government policy. In response to a Safermedia conference entitled "The harm that pornography does" (in which Westminster politicians were urged to look to the actions of the Chinese government during the Beijing Olympics as evidence that the internet can be regulated), the Department for Education invited the group to contribute to its review of sexualisation, which was led by Reg Bailey, chief executive of yet another Christian organisation, the Mothers' Union.

As there is little academic research into "sexualisation", much of the debate is based on anecdotal evidence or spurious surveys carried out by lifestyle magazines. It may well be a real phenomenon that needs to be addressed – possibly through legislative change – but until a consensus is reached on a definition, the term is adaptable to widely differing political agendas, some progressive, some authoritarian.

The views of such groups should not be dismissed simply because they are religiously inspired. If children really are being harmed by explicit material then it hardly matters whether campaigners are driven by faith or feminism. But those concerned about the rights of young people – and that includes the right to be free from homophobic bullying, to access safe sexual health services and to obtain contraception – should think carefully before forming alliances with lobbyists whose hardline moral stance puts those very rights at risk.